The present invention is directed to a technique for coating glass containers, and more particularly to a technique for applying color coatings that singularly or together may be colored, block ultra-violet light, and offer a range of surface textures.
The glass container industry limits itself to three primary colors for containers: clear glass (commonly called flint glass), amber and green. The green and amber are melted in several hues for both product differentiation and protection of the contents from the adverse effects of transmitted visual light as well as the ultra-violet component of natural and artificial light. Significant cost resulting from lost production when a glass melting unit changes from one color to another is experienced throughout the industry as well as the cost to carry inventory of containers made of a specific color during a run of a few weeks that will satisfy many months of need. There is also an ongoing cost of glass raw materials necessary for coloring, as well as the additional cost of storage silos and batch material weighing apparatus. In addition, extra fuel is required to melt colored glass batch. Also, the melting furnace life is reduced by the corrosive action of colored glass batches.
Recycling of glass containers has become a very popular and cost effective way to deal with empty glass container disposal. One problem of the existing system is the need to segregate the various colors of glass so as not to contaminate the different glass melts. This segregation requires three separate systems from the empty container receiving station throughout all of the handling up to and including the charging of the melting unit with the proper color glass. Introduction of expensive machinery is required to separate containers collected without segregation.
It is common practice in the glass industry to treat the outer surface of the containers with materials to counteract the effects of high glass-to-glass friction experienced on freshly manufactured glass products. Glass containers are conveyed with a great deal of glass-to-glass contact and at times considerable line pressure. Without treatment there is considerable visible scratching which may result in breakage. It is common to surface treat at two (2) locations in the operation. Immediately after forming and before lehring, the containers pass through a vapor which leaves a tin oxide film bonded to the surface. After lehring, the containers are sprayed with a dilute water solution of a material which, after evaporation of the water, leaves a film to provide surface lubricity. Of the two treatments, the tin oxide film is most costly, both for materials and system maintenance. The lubricity of the second film, though needed to prevent surface damage, may cause problems in subsequent labeling of the container.
There is an ongoing program in the container industry to reduce the weight of the container by reducing wall thickness, but still maintain acceptable product strength for both the internal pressures of carbonated beverages and the impact strength to survive handling damage in the filling operations, in the market place and by the consumer. The benefits of reduced weight are economic: lower glass melting fuel and material costs, higher container manufacturing speeds (lower cost) and reduced product shipping costs.